U.S. patent number 6,604,366 [Application Number 10/247,195] was granted by the patent office on 2003-08-12 for solid cryogen cooling system for focal plane arrays.
This patent grant is currently assigned to Raytheon Company. Invention is credited to Kent P Pflibsen.
United States Patent |
6,604,366 |
Pflibsen |
August 12, 2003 |
Solid cryogen cooling system for focal plane arrays
Abstract
A cryogenic cooling system (12) for cooling electromagnetic
energy detectors (50). The cooling system (12) includes a first
mechanism (18) that accommodates cryogen fluid in one or more
spaces (58, 60). A second mechanism (16, 42) freezes the cryogen
fluid in the one or more spaces (58, 60) adjacent to the
electromagnetic energy detectors (50). In a specific embodiment,
the electromagnetic energy detectors (50) comprise an infrared
focal plane array (50). The second mechanism (16, 42) includes a
heat exchanger (16) that is mounted separately from the first
mechanism (18). The one or more spaces (58, 60) are fitted with
three-dimensional cooling interface surfaces (62, 64). The
three-dimensional cooling surfaces (62, 64) are implemented via a
thermally conductive matrix (62, 64). The thermally conductive
matrix (62, 64) is a copper metal matrix or carbon/graphite matrix,
and the solid cryogen reservoir (18) is a beryllium reservoir (18).
The solid cryogen reservoir (18) includes integrated mounting
features (52, 54) for mounting the reservoir (18) to a missile
housing and a surface for attaching the focal plane array (50) to
the reservoir (18). The second mechanism (16, 42) includes a
Joule-Thomson orifice (42) that employs the Joule-Thomson effect to
cool the cryogen fluid to a solid state. The first mechanism (18)
includes a selectively detachable cryogen canister that provides
pressurized cryogen fluid to the heat exchanger (16). The heat
exchanger (16) directs cooled pressurized cryogen fluid to the
solid cryogen reservoir (18) and Joule-Thomson orifice (42) and is
positioned remotely from the cryogen reservoir (18). In an
illustrative embodiment, the heat exchanger (16) outputs cooled
cryogen gas to plural solid cryogen reservoirs (18) to cool plural
corresponding infrared focal plane arrays (50). A line cutter
selectively detaches the gas canister and/or the heat exchanger
(16) from the missile in response control signal from a computer.
The computer generates the control signal after a predetermined
amount of the cryogen fluid is present in the cryogen reservoir
(18) or after a predetermined time interval.
Inventors: |
Pflibsen; Kent P (Tucson,
AZ) |
Assignee: |
Raytheon Company (Lexington,
MA)
|
Family
ID: |
27662788 |
Appl.
No.: |
10/247,195 |
Filed: |
September 19, 2002 |
Current U.S.
Class: |
62/53.2; 62/54.2;
62/54.3 |
Current CPC
Class: |
G01S
3/781 (20130101) |
Current International
Class: |
G01S
3/781 (20060101); G01S 3/78 (20060101); F17C
013/08 () |
Field of
Search: |
;62/46.1,47.1,48.1,53.2,54.2,54.3,601 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Esquivel; Denise L.
Assistant Examiner: Drake; Malik N.
Attorney, Agent or Firm: Finn; Thomas J. Raufer; Colin M.
Lenzen, Jr.; Glenn H.
Claims
What is claimed is:
1. A cryogenic cooling system for cooling electromagnetic energy
detectors comprising first: first means for accommodating cryogen
fluid in one or more spaces and second means for freezing said
cryogen fluid in said one or more spaces adjacent to said
electromagnetic energy detectors.
2. The system of claim 1 wherein said electromagnetic energy
detectors comprise one or more focal plane arrays.
3. The system of claim 2 wherein said second means includes a heat
exchanger that is mounted separately from said first means.
4. The system of claim 3 wherein said heat exchanger is adapted to
cool plural focal plane arrays.
5. The system of claim 2 wherein said one or more spaces are fitted
with three-dimensional surfaces or cryogen absorbents.
6. The system of claim 2 wherein said first means includes a solid
cryogen reservoir having a thermally conductive matrix with said
one or more spaces formed therein.
7. The system of claim 6 wherein said thermally conductive matrix
is a copper metal matrix, and said solid cryogen reservoir is a
beryllium reservoir.
8. The system of claim 7 wherein said matrix includes one or more
pins or flanges.
9. The system of claim 7 wherein said solid cryogen reservoir
includes one or more mounting features and a surface for mounting a
focal plane array.
10. The system of claim 6 wherein said second means includes means
for employing the Joule-Thomson effect to cool said cryogen fluid
from a gas state to a saturated state.
11. The system of claim 10 wherein said first means includes a
selectively detachable cryogen canister for providing pressurized
cryogen fluid to a heat exchanger, said heat exchanger in fluid
communication with said solid cryogen reservoir.
12. The system of claim 11 wherein said heat exchanger is
positioned remotely from said cryogen reservoir.
13. The system of claim 12 wherein said heat exchanger is a single
heat exchanger that outputs cooled cryogen gas to plural solid
cryogen reservoirs to cool plural corresponding infrared focal
plane arrays.
14. The system of claim 1 wherein said cryogenic cooling system is
mounted on or within a missile system and is adapted to cool an
infrared focal plane array.
15. The system of claim 14 wherein said cryogenic cooling system
includes a cryogen canister and a heat exchanger for providing said
cryogen fluid to a cryogen reservoir incorporating said one or more
spaces and employing the Joule-Thomson effect to produce liquid
cryogen that is later frozen in the reservoir.
16. The system of claim 15 wherein said heat exchanger is
positioned separately from said reservoir and employs a conduit to
direct said cryogen fluid to said cryogen reservoir.
17. The system of claim 16 wherein said heat exchanger feeds plural
cryogen cooling interfaces attached to plural corresponding
infrared focal plane arrays.
18. The system of claim 17 further including means for selectively
detaching said gas canister and said heat exchanger from said
missile after a predetermined amount of said cryogen fluid is
within said cryogen reservoir or after a predetermined time
interval.
19. A cryogenic cooling system for cooling electromagnetic energy
detectors comprising: first means for accommodating cryogen fluid
in a space having a three-dimensional thermally conductive surface
and second means for freezing said cryogen fluid in said space
adjacent to said electromagnetic energy detectors, said second
means employing a heat exchanger for initiating cooling of said
cryogen fluid, said heat exchanger positioned remotely from said
first means.
20. The system of claim 19 wherein said heat exchanger is adapted
to provide said cryogen fluid to plural spaces associated with
different cooling interfaces included in said first means for
cooling plural focal plane arrays.
21. The system of claim 20 wherein said second means includes a
Joule-Thomson orifice.
22. A cryogenic cooling system for cooling an array of detectors
comprising: first means for maintaining a cryogen fluid at a first
pressure and selectively outputting said cryogen fluid at a second
pressure sufficiently lower than said first pressure to promote
conversion of said cryogen fluid to a solid state and second means
for receiving said cryogen fluid output from said first means and
maintaining said cryogen fluid in plural adjacent volumetric
sections next to said array of detectors as said cryogen fluid
freezes.
23. The system of claim 22 wherein said first means includes a
cryogen canister that is selectively detachable from said cryogenic
cooling system.
24. The system of claim 23 wherein said first means includes a heat
exchanger.
25. The system of claim 24 wherein said second means includes a
cryogen cooling interface abutting an infrared focal plane array,
said cryogen cooling interface mounted separately from said heat
exchanger.
26. A cryogenic cooling system for cooling an infrared focal plane
array of detectors comprising: a heat exchanger for removing
sufficient heat from a cryogen fluid to promote liquefaction of
said cryogen fluid, said heat exchanger positioned remotely from
said infrared focal plane array of detectors and a cooling
interface adjacent to said infrared focal plane array of detectors
and in fluid communication with said heat exchanger, said cooling
interface having a space with a three-dimensional surface designed
to accommodate said cryogen fluid as said cryogen fluid transforms
to a solid state.
27. A cooling arrangement for a focal plane array of detectors,
said arrangement comprising: a cooling interface thermally coupled
to said focal plane array and frozen cryogen disposed within said
cooling interface.
28. The invention of claim 27 wherein said arrangement further
includes means for maintaining said cryogen in a frozen solid
state.
29. A cryogenic cooling system for cooling electromagnetic energy
detectors comprising: first means for accommodating cryogen fluid
in one or more spaces, said first means thermally coupled to said
electromagnetic energy detectors and second means for freezing said
cryogen fluid in said one or more spaces.
30. A method for cooling electromagnetic energy detectors to
cryogenic temperatures comprising: accommodating cryogen fluid in
one or more spaces and freezing said cryogen fluid in said one or
more spaces adjacent to said electromagnetic energy detectors.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to cooling systems. Specifically, the
present invention relates to cryogenic cooling systems for cooling
focal plane arrays.
2. Description of the Related Art
Cryogenic cooling systems are employed in various demanding
applications including military and civilian active and remote
sensing, superconducting, and general electronics cooling. Such
applications often demand efficient, reliable, and cost-effective
cooling systems that can achieve extremely cold temperatures below
80 degrees Kelvin.
Efficient cryogenic cooling systems are particularly important in
sensing applications involving high-sensitivity infrared focal
plane arrays of electromagnetic energy detectors (FPA's). An FPA
may detect electromagnetic energy radiated or reflected from a
scene and convert the detected electromagnetic energy into
electrical signals corresponding to an image of the scene. To
optimize FPA imaging performance, any FPA detector nonuniformities,
such as differences in individual detector offsets, gains, or
frequency responses, are corrected. Any spatial or temporal
variations in temperature across the FPA may cause prohibitive FPA
nonuniformities.
FPA's are often employed in missile targeting applications, where
weight, size, and spatial and temporal uniformity of cryogenic
cooling systems are important design considerations. An FPA must
operate at stable cryogenic temperatures for maximum performance
and sensitivity.
Conventionally, a cooling fluid is applied to the FPA via a cooling
interface. Heat is transferred to the cooling fluid from the FPA.
The heated fluid is then expelled from the missile or re-cooled via
a heat exchanger integrated into the FPA. The cooling fluid
requires a heavy and bulky FPA cooling interface and heat
exchanger, which are attached to the FPA mounting assembly.
Consequently, the FPA assembly must have additional mechanical
support to secure the interface, heat exchanger, and cooling fluid.
The bulky components and additional support hardware may require
additional cooling, which increases demands placed on the cooling
system. The bulky support structure, conventionally thought to
improve temperature stability, may conduct excess heat from the
warm missile body into the FPA, thereby reducing system cooling
efficiency. Furthermore, the additional bulky mechanical FPA
support hardware may cause alignment problems with the on board
optical or infrared system during installation and operation,
thereby increasing installation and operating costs. In addition,
missile maneuvering may cause the cooling liquid to slosh in the
cooling interface, creating undesirable temperature
instabilities.
Alternatively, Joule-Thompson cycle coolers are employed. A
Joule-Thomson cycle cooler typically applies a regulated flow of
cold gas over the infrared FPA. However, Joule-Thompson cycle
coolers require undesirably expensive and bulky compressed gas
canisters that must remain on the missile, aircraft, or other
system. The additional weight increases the overall operating costs
and reduces maneuvering capability and range of the accompanying
system. Furthermore, excessive shock or vibration environments from
missile maneuvering may interrupt gas flow, thereby creating
potentially prohibitive temperature instabilities, resulting in
reduced missile performance.
To address size and cost issues associated with using gas
canisters, compressors, or other heat exchangers, more advanced
construction materials are under continual development. In
addition, researchers are attempting to design FPA's with reduced
cooling requirements. Unfortunately, this has matured slowly and
does not promise satisfactory solutions for high performance
applications in the foreseeable future.
Hence, a need exists in the art for an efficient cryogenic cooling
system for uniformly cooling an infrared FPA. There exists a
further need for a cryogenic cooling system that efficiently
employs a solid cryogen to cool an FPA with minimal weight and size
impact.
SUMMARY OF THE INVENTION
The need in the art is addressed by the cryogenic cooling system
for cooling electromagnetic energy detectors of the present
invention. In the illustrative embodiment, the inventive system is
adapted to cool infrared focal plane arrays. The system includes a
first mechanism for accommodating cryogen fluid in one or more
spaces. A second mechanism freezes the cryogen fluid in the one or
more spaces adjacent to the electromagnetic energy detectors.
In a more specific embodiment, the electromagnetic energy detectors
comprise one or more focal plane arrays. The second mechanism
includes a heat exchanger that is mounted separately from the first
mechanism. The one or more spaces are fitted with three-dimensional
cooling interface surfaces. The first mechanism includes a solid
cryogen reservoir having a thermally conductive matrix for
implementing the three-dimensional cooling surfaces. The thermally
conductive matrix is a copper, graphite, or beryllium matrix, and
the solid cryogen reservoir is a beryllium reservoir.
The solid cryogen reservoir includes one or more mounting features
for mounting the reservoir and has a surface for mounting the focal
plane array on the reservoir. The second mechanism includes a
mechanism for employing the Joule-Thomson effect (also called the
Joule-Kelvin effect) to cool the cryogen fluid to a liquid state.
The first mechanism includes a selectively detachable cryogen
canister for providing pressurized cryogen fluid to the heat
exchanger.
In an illustrative embodiment, the heat exchanger outputs cooled
cryogen gas to plural solid cryogen reservoirs to cool plural
corresponding infrared focal plane arrays. The cryogenic cooling
system is mounted on or within a missile system. The cryogenic
cooling system is connected to a cryogen canister and a heat
exchanger for providing the cryogen fluid to a cryogen reservoir
with three-dimensional cooling surfaces. A Joule-Thomson orifice
employs the Joule-Thomson effect to create the cryogen fluid output
from the heat exchanger.
The heat exchanger, which is positioned separately from the
reservoir, employs a conduit to direct the fluid to the cryogen
reservoir. An additional mechanism selectively detaches the gas
canister and/or the heat exchanger from the missile after a
predetermined amount of the fluid is collected within the cryogen
reservoir or after a predetermined time interval.
The novel design of the present invention is facilitated by the
second mechanism, which freezes cryogen in a cooling interface
adjacent to a focal plane array. Freezing the cryogen enables
remote positioning of the heat exchanger relative to the cooling
interface. The cooling interface and accompanying focal plane array
assembly no longer require mounting of the heat exchanger in the
same assembly to increase the temperature stability of the focal
plane array. The frozen cryogen in combination with the efficient
solid cryogen cooling interface of the present invention provides
sufficient temperature stability. Consequently, costs, cooling
inefficiencies, and sensor alignment problems associated with
conventional cooling systems are avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a missile system employing a solid
cryogen infrared Focal Plane Array (FPA) cooling system constructed
in accordance with the teachings of the present invention.
FIG. 2 is a perspective view showing the heat exchanger and solid
cryogen cooling interfaces of the solid cryogen cooling system of
FIG. 1.
FIG. 3 is a perspective view showing an alternative embodiment of a
cryogen cooling interface and accompanying FPA assembly of FIG.
2.
DESCRIPTION OF THE INVENTION
While the present invention is described herein with reference to
illustrative embodiments for particular applications, it should be
understood that the invention is not limited thereto. Those having
ordinary skill in the art and access to the teachings provided
herein will recognize additional modifications, applications, and
embodiments within the scope thereof and additional fields in which
the present invention would be of significant utility.
FIG. 1 is a diagram of a missile system 10 employing a solid
cryogen infrared Focal Plane Array (FPA) cooling system 12
constructed in accordance with the teachings of the present
invention. For clarity, various well-known components, such as
power supplies, actuators, heat exchanging coils, explosives
compartments, and so on, have been omitted from the figures.
However, those skilled in the art with access to the present
teachings will know which components to implement and how to
implement them to meet the needs of a given application.
The cooling system 12 includes a pressurized cryogen gas canister
14, a heat exchanger 16, a solid cryogen FPA cooling interface 18,
temperature sensors 20, a missile computer 22, and a line cutter
24. The heat exchanger 16 is connected to the pressurized cryogen
gas canister 14 via a high-pressure input line 26 that is connected
to an electrically controlled valve 28 at the output of the gas
canister 14. An exhaust output line 30 is connected to the heat
exchanger 16 at one end and to a flange 32 at the opposite end. The
exhaust flange 32 is attached to a wall of the missile 10 so that
exhaust gases may escape from the missile 10. The exhaust output
line 30 includes a flexible bellows 34 to provide mechanical and
thermal isolation of the heat exchanger 16 from exhaust flange 32
and body of the missile 10. The flexible exhaust bellows 34 may or
may not include a pump depending on the demands of a given
application.
The heat exchanger 16 is connected to the solid cryogen FPA cooling
interface 18 via a flexible output pressure line 36 and an input
exhaust line 38. A sensor suite 40 is mounted on the FPA cooling
interface 18. One or more temperature sensors 20 provide
temperature input to the missile computer 22, which may send
control signals to the line cutter 24 and to the electronically
actuated cryogen canister valve 28.
In operation, the missile computer 22 activates the cooling system
12 by opening the electrically controlled valve 28 via a control
signal sent thereto. Pressurized cryogen gas is then transferred to
the heat exchanger 16 via the high-pressure line 26. The
pressurized cryogen gas passes through various heat exchanging
coils or other heat-exchanging mechanisms in the heat exchanger 16
before being transferred to the FPA cooling interface 18 via the
output pressure line 36. On the initial pass, the pressurized
cryogen gas is not optimally cooled by the heat exchanger 16, since
cooling exhaust gasses have not yet been generated to facilitate
cooling of the input cryogen gas.
The pressurized cryogen gas entering the FPA cooling interface 18
passes through a Joule-Thomson orifice 42, where the gas is
depressurized as it enters the FPA cooling interface 18. Due to the
Joule-Thomson effect, the depressurized gas passing through the FPA
cooling interface 18 becomes sufficiently cold to enter a saturated
state and liquefy. Any liquid cryogen that is caught in the FPA
cooling interface 18 eventually freezes. Remaining gas that has not
liquefied in the cooling interface 18 is directed back through the
heat exchanger 16 via the input exhaust line 38.
Unlike conventional systems, the heat exchanger 16 is remotely
positioned relative to the cryogen FPA cooling interface 18 and
accompanying sensor suite 40. This facilitates mounting of the
sensor suite 40 and accompanying FPA's via smaller, lighter, and
more cost-effective mounting structures.
By connecting the heat exchanger 16 to the FPA cooling interface 18
via the flexible pressure line 36 and the exhaust line 38 having a
flexible coupling 44 included therein, the motion and vibration of
the relatively heavy heat exchanger 16 is isolated from the sensor
suite 40 and accompanying FPA cooling interface 18. Consequently,
abrupt missile maneuvers that move the heavy heat exchanger 16 are
less likely to disrupt operations of the sensor suite 40. The
flexible exhaust coupling 44 may include a pump to facilitate
circulation of exhaust gases in the cooling system 12.
Cold cryogen exhaust gas returning from the FPA cooling interface
18 cools incoming pressurized gas in the heat exchanger 16. This
process raises the temperature of the exhaust gas, which is
directed out of the missile 10 via the output exhaust line 30.
Some depressurized cryogen gas passing through the FPA cooling
interface 18 eventually liquefies and then freezes in the FPA
cooling interface 18. After cessation of gas flow, the internal
pressure of the FPA cooling interface 18 decreases, enabling the
liquid to boil and causing the cryogen in the FPA cooling interface
18 to freeze. The solidified cryogen improves temperature stability
across the cooled FPA's in the sensor suite 40. The temperature
remains relatively constant in time and position across the surface
of a cooled FPA. By employing the special cryogen FPA cooling
interface 18 to cool an FPA via solid cryogen, both temporal and
spatial temperature stability are enhanced. This may significantly
enhance the operation of the FPA and accompanying sensor suite 40.
This may also simplify nonuniformity correction circuitry and
algorithms required to compensate for FPA detector
nonuniformities.
In the present specific embodiment, the cryogen gas is Argon.
However, other types of cryogen gas, such as Krypton, Nitrogen,
Neon, or Hydrogen, may be employed without departing from the scope
of the present invention.
Strategically positioned temperature sensors 20 enable software
running on the missile computer 22 to determine when the cooling
interface 18 has reached a desired temporal and spatial temperature
stability and/or uniformity. The software running on the missile
computer 22 then actuates the line cutter 24, which cuts the input
pressure line 26, enabling the pressurized cryogen gas canister 14
to release from the missile 10. The missile 10 continues flying as
frozen cryogen in the FPA cooling interface 18 continues to
efficiently cool the FPA's in the sensor suite 40.
Hence, the missile computer 22 runs software to actuate the line
cutter 24 when the solid cryogen FPA cooling interface 18 reaches a
predetermined temperature and/or spatial and temporal temperature
stability and uniformity as determined via the temperature sensors
20. Those skilled in the art with access to the present teachings
may easily construct this software without undue
experimentation.
Those skilled in the art will appreciate that various modules shown
in FIG. 1 may be omitted or replaced with other types of modules
without departing from the scope of the present invention. For
example, the temperature sensors 20 for determining when to actuate
the line cutter 24 may be replaced with a timer or mechanical
mechanism to determine when to actuate the line cutter 24.
Furthermore, the missile computer 22, the electrically controlled
nozzle 28, and/or the line cutter 24 may be omitted in various
applications, such as those that do not require the release of the
pressurized cryogen gas canister 14 from the missile 10. In
addition, some applications may demand that the heat exchanger 16
be released from the missile 10 along with the pressurized cryogen
gas canister 14 when sufficient solid cryogen forms in the FPA
cooling interface 18. In this implementation, line cutters may be
employed to cut the input exhaust line 38 and the output pressure
line 36.
A method adapted for use with the missile 10 and accompanying
cryogenic cooling system 12 includes the following steps: 1. Launch
the missile 10. 2. Open valve 28 to release pressurized cryogen gas
from the cryogen gas canister 14 to the heat exchanger 16. 3.
Employ the heat exchanger 16 to cool the incoming pressurized gas.
4. Depressurize the gas via a Joule-Thomson orifice 42 to release a
freezing fluid in a solid cryogen cooling interface 18 having an
integrated infrared FPA that is mounted remotely relative to the
heat exchanger 16. 5. Collect any resulting liquefied fluid in the
solid cryogen interface 18 adjacent to an IR FPA, directing any
remaining cold gaseous fluid (exhaust gas) back through the heat
exchanger 16. 6. Use the cold exhaust gas to cool incoming
pressurized gas in the heat exchanger 16 before expelling the cool
exhaust gas from the missile 10. 7. After a predetermined amount of
liquid cryogen is accumulated in the solid cryogen interface 18,
cut the pressure line 26 to the cryogen gas canister 14. 8. Release
the cryogen gas canister from the missile 10 and allow the liquid
cryogen to boil, thereby cooling the cryogen to a solid.
Those skilled in the art will appreciate that some of the above
steps may be omitted or interchanged with other steps without
departing from the scope of the present invention. For example, the
electrically controlled valve 28 at the output of the cryogen gas
canister 14 may be opened before the missile 10 is launched, and
steps 7 and 8, wherein the cryogen gas canister 14 is released from
the missile 10 may be omitted in some applications.
FIG. 2 is a perspective view showing the heat exchanger 16 and two
exemplary solid cryogen cooling interfaces 18 of the solid cryogen
cooling system 12 of FIG. 1. The input pressure line 26 is split
into two output pressure lines 36 within the heat exchanger 16. The
output pressure lines 36 are fed to corresponding solid cryogen FPA
cooling interfaces 18.
The heat exchanger 16 may be adapted to accommodate several cooling
interfaces. To accommodate a third cooling interface (not shown),
the input pressure line 26 is separated into three output pressure
lines, and the additional line goes to the third cooling interface.
In the present specific embodiment, each cooling interface 38 has a
separate return exhaust line 38. The separate exhaust lines 38 feed
cold exhaust gasses back to the heat exchanger 16 to cool incoming
pressurized gas before being expelled from the missile 10 of FIG. 1
via the flexible bellows 34 and flange 32 of the output exhaust
line 30. The flex couplings 44 on the input exhaust lines 38 help
isolate vibrations and movement of the heat exchanger from focal
plane arrays 50 integrated with the cooling interfaces 18.
Remotely positioning the heat exchanger 16 from the cryogen cooling
interfaces 18 allows the single heat exchanger 16 to accommodate
plural cooling interfaces 18. This results in substantial size,
weight, and cost savings, as fewer parts are required, which
results in fewer installation, mounting, and FPA alignment
problems. The ability to remotely position the heat exchanger 16
relative to the cooling interfaces 18 is facilitated by the use of
solid cryogen, which is collected in the cooling interfaces 18.
When disposed in the cooling interfaces 18, the solid cryogen
provides sufficient spatial (or volumetric) and temporal
temperature stability across the infrared FPA's 50 to obviate the
need to incorporate the massive heat exchanger 16 into the FPA
mounting assembly and cooling interface 18. The efficient design of
the cooling interfaces 18 enables the cooling interfaces 18 to act
as both infrared FPA mounting assemblies and cooling interfaces.
The FPA assemblies 50 are integrated with the cooling interfaces
18.
The cooling interfaces 18 each include two side mounting features
52 and a front mounting feature 54 to facilitate stabilizing the
cooling interfaces 18 within the body of the missile 10 of FIG. 1.
In the present specific embodiment, the mounting features 52 and 54
are constructed from the same block of material as the cooling
interfaces 18. The mounting features may be fitted with thermal
insulation to prevent heat from transferring from the missile body
to the cooling interfaces 18. Hence, the solid cryogen cooling
interfaces 18 efficiently integrate mounting features 52 and 54 and
surfaces for mounting the FPA's 50 into single pieces 18.
The cooling interfaces 18 include Joule-Thomson orifices 42, which
release pressurized gas from the output pressure lines 36 into the
cooling interfaces 18. As the cryogen gas exits the pressure lines
36 and passes into the interfaces 18 via the Joule-Thomson orifices
42, the gas depressurizes sufficiently to initiate partial
liquefaction of the cryogen gas in the interfaces 18. Some of the
liquefied cryogen is caught in the cooling interfaces 18 where it
accumulates. After cessation of gas flow, the pressure in the
cooling interfaces 18 is reduced, which allows a portion of the
stored cryogenic liquid to boil, thereby cooling the remaining
liquid until it freezes.
Each cooling interface 18 has a first cooling section 58 in fluid
communication with a second cooling section 60. Input cryogen gas
is released from the Joule-Thomson orifice 42 into the first
cooling section 58 before passing to the second cooling section 60.
For illustrative purposes, top surfaces of the cooling interfaces
18 are removed. In an actual implementation, the first section 58
and second section 60 are enclosed in the cooling interfaces 18. In
this realization, all cryogen gas entering the Joule-Thomson
orifice 42 and not liquefying in the cooling sections 58 and 60 is
transferred via the exhaust line 38 back to the heat exchanger 16.
One skilled in the art will appreciate that the exhaust gases
exiting from the second cooling section 60 may pass directly out of
the missile without passing first through the heat exchanger 16.
This may further simplify the configuration of the exhaust line 38
and allow the pressure within the cooling interface 18 to be
reduced, thereby allowing the operating temperature of the solid
cryogen to be reduced. While the utilization of the high pressure
cryogenic gas may be less efficient in this implementation, a lower
ultimate operating temperature may be achieved. The lost efficiency
may be partially regained by adding a second cryogen gas flow to
the heat exchanger 16. This gas flow passes through a
Joule-Thompson orifice (not shown) within the heat exchanger 16 and
provides cooling of the cryogen gas passing through the heat
exchanger 16 and then to the cooling interfaces 18 via the pressure
lines 36.
The first cooling section 58 represents a partial indentation in a
cooling interface housing 66. The first cooling section 58 is
formed in the cooling interface housing 66 opposite the FPA 50,
which is mounted on a reverse side of the cooling interface housing
66. The first cooling section 58 includes several pins 62, which
are integral to the beryllium cooling interface housing 66. The
pins 62 are strategically positioned and shaped to promote
efficient thermal transfer between cryogen passing through the
first cooling section 58 and the beryllium cooling interface
housing 66. The pins 62 form a metal matrix with plural spaces or
compartments formed between the pins 62. The plural compartments
expand the thermally conductive surface area of the first section
58 and facilitate efficient cooling of the FPA 50. The exact number
of pins and the sizes and shapes of the pins 62 are
application-specific and may be determined by one skilled in the
art with access to the present teachings to meet the needs of a
given application.
The second cooling section 60 receives cold cryogen gas from the
first cooling section 58. Cryogen gas that has not been trapped as
frozen or liquefied cryogen in the first section 58 flows into the
second section 60. The second section 60 includes plural flanges 64
designed to optimize thermal transfer between liquid and solid
cryogen freezing in the second section 60 and the FPA 50. The
plural compartments formed between the flanges 64 ensure that
sufficient surface area of the cooling interface 18 contacts the
frozen cryogen to achieve optimum FPA temperature stability. The
relatively large volume of the second section 60 promotes long hold
time and temperature stability of the FPA 50. Those skilled in the
art will appreciate that the second section 60 may be omitted in
some applications without departing from the scope of the present
invention.
The first section 58 and the second section 60 accommodate
three-dimensional surfaces formed by the pins 62 and the absorber
flanges 64, respectively. The absorber flanges 64 may be replaced
with another type of absorbent structure, such as a thermally
conductive matrix or mesh absorbent, without departing from the
scope of the present invention. For the purposes of the present
discussion, a three dimensional surface is a surface that includes
a plurality of surface dips, grooves, contours, or compartments for
expanding the surface area over that of a substantially flat
surface.
The cooling sections 58 and 60 and the infrared FPA 58 are
positioned so that cold incoming cryogen gas initially cools the
first section 58, thereby cooling the FPA 50 first before being
warmed by other features. This improves the efficiency of the
cryogen cooling interface 18 by ensuring that the first section 58,
which is adjacent to the FPA 50, remains at a spatially and
temporally stable cryogenic temperature at or below 80 degrees
Kelvin.
The second section 60 of the cooling interfaces 18 eventually
contain solid cryogen. Unlike gas or liquid cooling systems, the
solid cryogen does not slosh in response to missile maneuvers.
Consequently, the cooling interface 18 can provide stable cryogenic
temperatures to the FPA, which are stable in time and uniform
across a given volume near the FPA 50.
The flanges 64 are brazed to the body of the second section 60.
Copper mesh or graphite fiber may be used. The fibrous nature of
the material prevents separation of the liquid and wicking material
from the housing. A material should be chosen that can be joined to
the housing of the cooling interfaces 18. The material should wick
the liquid cryogen efficiently to prevent it from being expelled
out of the exhaust lines 38 when high-volume cryogen gas flow is
occurring.
Those skilled in the art will appreciate that the copper pins 62 in
the first cooling section 58 and the cooling flanges 64 in the
second section 60 may be replaced with other features without
departing from the scope of the present invention. For example, the
pins 62 in the first cooling section 58 may be replaced with a
sintered or foamed metal matrix, such as a metallic sponge,
constructed via a sintering or a metal or graphite foaming process.
The pins 62 may represent a copper metal matrix or a
carbon/graphite matrix.
Employing frozen cryogen in the efficient solid cryogen cooling
interfaces 18 to cool the infrared FPA's 50 allows the heat
exchanger 16 to be positioned remotely from the FPA's 50 and
corresponding mounting structure 66. The large mass of the heat
exchanger 16 is no longer required to increase the temperature
stability of the FPA's 50, since the frozen cryogen trapped in the
efficient cooling interfaces 18 provides sufficient temperature
stability. Unlike the heat exchanger 16, which is connected to the
cooling interfaces 18 and FPA assemblies 58 only via the pressure
lines 36 and exhaust lines 38 and is mounted separately from the
cooling interfaces 18, conventional systems employ one heat
exchanger for each FPA to be cooled. In these systems, a heat
exchanger is mounted to each FPA assembly and/or cooling interface.
This increases installation and parts costs and may create sensor
alignment difficulties.
FIG. 3 is a perspective view showing an alternative embodiment of a
cryogen cooling interface 18' and accompanying FPA assembly 68. The
operation of the cryogen cooling interface 18' is similar to the
operation of the cryogen cooling interfaces 18 of FIG. 2 with the
exception that the pins 62 of FIG. 2 are replaced with vertically
oriented rectangular cooling plates 70, and the infrared FPA 50 of
FIG. 2 is replaced with a more elaborate infrared FPA assembly 68.
Furthermore, the mounting features 52 and 54 of FIG. 2 are omitted
from the cooling interface 18' of FIG. 3. The rectangular cooling
plates 70 form various volumetric sections 76 to promote heat
transfer away from the FPA assembly 68.
The FPA assembly 68 includes an additional saw-toothed fitting 72
designed to mate with and help stabilize a corresponding FPA
assembly support structure 74. In addition, the ridged fitting 72
promotes the conduction of heat away from FPA assembly 68 to the
cooling interface 18'. The FPA assembly 68 is efficiently
integrated with cooling interface 18' to provide excellent
temperature stability.
Thus, the present invention has been described herein with
reference to a particular embodiment for a particular application.
Those having ordinary skill in the art and access to the present
teachings will recognize additional modifications, applications,
and embodiments within the scope thereof.
It is therefore intended by the appended claims to cover any and
all such applications, modifications and embodiments within the
scope of the present invention.
Accordingly,
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